1. Field of the Invention
This invention relates to a process for the preparation of hydroquinone and is more particularly concerned with a process for the oxidation of p-substituted phenols to hydroquinone and with processes for the conversion of phenol to hydroquinone which incorporate this oxidation as a step therein.
2. Description of the Prior Art
Hydroquinone, and its preparation by a wide variety of methods, are well known in the art. The principal methods which have received commercial attention include (i) the reduction of quinone (obtained either by oxidation of aniline or the electrolytic oxidation of benzene); (ii) the hydrolysis of p-halogenated phenols; (iii) hydroperoxidation of p-dialkylbenzenes followed by acid hydrolysis; and (iv) the oxidation of esters of 4-(.alpha.,.alpha.-dialkylmethyl)phenols followed by acid cleavage of the resulting hydroperoxides. Illustrative of the latter method is the oxidation of the acetate of p-isopropylphenol to the corresponding hydroperoxide followed by acid cleavage of the latter to give a mixture of hydroquinone and acetone: see U.S. Pat. No. 3,028,410.
I have now found that p-isopropenylphenol and related phenols having in the para-position a 1-cycloalkenyl or an .alpha.-methylene-(alkyl or aralkyl) group can be readily converted to a mixture of hydroquinone and the appropriate ketone in high yield and in a one step reaction. I have found further that this process of my invention is particularly useful in a cyclic process in which phenol is condensed with acetone to yield bisphenol A, the bisphenol A is subjected to alkaline hydrolysis to yield a mixture of phenol and p-isopropenylphenol, the latter is subjected to the process of the invention to obtain hydroquinone and acetone, and the acetone and phenol regenerated in the various stages of the process are re-used in a further cycle of operations.